Functional fluid compositions

ABSTRACT

Production of functional fluids, including aircraft hydraulic fluids and aircraft engine lubricants of improved fire resistance, comprising a functional fluid base stock, such as a phosphate ester, e.g., tri-n-butyl phosphate, di-n-butyl phenyl phosphate, or mixtures thereof, and/or a dicarboxylic acid ester, e.g., a diester of adipic acid such as diisodecyl adipate, or mixtures of such phosphate ester or esters, and dicarboxylic acid ester, and a small amount of an organic iodo compound such as iodobiphenyl or iodonaphthalene.

Unite States atent Sheratte Jan. 21, 1975 [73] Assignee: McDonnellDouglas Corporation,

Santa Monica, Calif.

[22] Filed: May 1, 1972 [21] Appl. No.: 249,413

[52] U.S. Cl 252/78, 252/49.9, 252/54.6, 252/58, 252/388, 252/399 [51]Int. Cl C09k 3/02 [58] Field of Search 252/78, 75, 49.9, 58, 399,252/388, 54.6; 260/989 2,934,50! 4/1960 Moreton 252/78 2,967,827 l/l96l3,287,275 l l/l966 3,591,506 7/1971 Peeler et al 252/78 PrimaryExaminer-Cameron K. Weiffenbach Attorney, Agent, or Firm-Max Geldin [57]ABSTRACT Production of functional fluids, including aircraft hydraulicfluids and aircraft engine lubricants of improved fire resistance,comprising a functional fluid base stock, such as a phosphate ester,e.g., tri-n-butyl phosphate, di-n-butyl phenyl phosphate, or mixturesthereof, and/or a dicarboxylic acid ester, e.g., a diester of adipicacid such as diisodecyl adipate, or mixtures of such phosphate ester oresters, and dicarboxylic acid ester, and a small amount of an organiciodo compound such as iodobiphenyl or iodonaphthalene.

27 Claims, No Drawings FUNCTIONAL FLUID COMPOSITIONS This inventionrelates to functional fluid compositions having improved fire resistanceand is particularly directed to compositions comprising certainfunctional fluids and an additive amount sufficient to improve fireresistance, of certain organic iodo compounds.

Many different type of materials are employed as functional fluids andfunctional fluids are utilized in a wide variety of applications. Thus,such functional fluids have been utilized as electronic Coolants,diffusion pump fluids, lubricants, damping fluids, power transmissionand hydraulic fluids, heat transfer fluids and heat pump fluids. Aparticularly important application of such functional fluids has beentheir utilization as hydraulic fluids and engine lubricants in aircraft,requiring successful operation of such fluids over a wide temperaturerange, a particularly important and highly desirable property of suchfluids being fire resistance.

Functional, e.g., hydraulic fluids, employed in many industrialapplications and particularly hydraulic fluids for aircraft must meet anumber of important requirements. Thus, such hydraulic fluidsparticularly for aircraft use, should be operable over a widetemperature range, should have good stability at relatively hightemperatures and preferably have lubricating characteristics. Inaddition to having the usual combination of properties making it a goodlubricant or hydraulic fluid, such fluid should also have relatively lowviscosity at extremely low temperatures and an adequately high viscosityat relatively high temperatures, and must have adequate stability at thehigh operating temperatures of use. Further, it is of importance thatsuch fluids be compatible with and not adversely affect or corrodematerials including metals and non-metals such as elastomeric seals ofthe system in which the fluid is employed. It is particularly importantin aircraft hydraulic fluids and lubricants that such fluids have ashigh a fire resistance as possible to prevent ignition if such fluidsare accidentally or as result of damage to the hydraulic system, sprayedonto or into contact with surfaces or materials of high temperatures.

While many functional and hydraulic fluid compositions have beendeveloped having most of the aforementioned required properties, many ofthese compositions do not have the requisite high fire resistancedesired particularly for use of such functional fluid or hydraulic fluidcompositions in modern high speed aircraft or in a hydraulic systemlocated near a high temperature jet-turbine power plant of a jet-turbineaircraft.

Thus, as an illustration, many functional and hydraulic fluids have anautoignition temperature ranging from about 450 to about 700F. It isparticularly desirable to increase the autoignition temperature of suchfunctional and hydraulic fluids above 750F, e.g., to the range of about800 to about l,000F.

It has now been found in accordance with the present invention that thefire resitance, or autoignition temperature, of functional fluid orhydraulic fluid compositions containing as base stock a phosphate esterand/or a dicarboxylic acid ester, or mixtures thereof, can besignificantly improved by the addition to such compositions of a smallamount of certain organic iodo compounds, e.g., in the form of certainalkyl or aryl iodides, especially aryl iodides, defined in greaterdetail hereinafter. The inclusion of such iodide additives in the abovefunctional and hydraulic fluid compositions generally does not adverselyaffect any of the above-noted important characteristics of such fluids,particularly aircraft hydraulic fluids, including their desirableviscosity characteristics. 1

lt has been found that certain aryl and alkyl iodides, and particularlythe aryl iodides of the invention described below, e.g., iodobiphenyl oriodonaphthalene, not only function to substantially increase autogenousignition (autoignition) temperature and reduce flaminability offunctional fluids and hydraulic fluids containing a phosphate and/ordicarboxylic acid ester base stock, as described above, but in additionhave the advantageous properties of being thermally stable, free fromtoxicity, cause substantially no corrosion of metal parts such asaluminum, iron, copper and titanium, do not have an objectionable odor,are only very slightly colored, and have sufficient solubility in theabove functional and hydraulic fluids to effectively function therein asflame inhibitors. In addition, the organic iodo compounds hereof,particularly the aryl derivatives, employed according to the invention,have no adverse effect on low temperature viscosity of the functionalfluids, particularly when employed as hydraulic fluids in aircraft, donot adversely affect the thermal stability of the fluid, and are ofrelatively low cost.

Effective organic iodo compounds for use as additive in the phosphateester and/or dicarboxylic acid ester functional or hydraulic fluids toreduce flammability and increase autoignition temperature of the fluid,according to the invention, are compounds having the formula RI where Ris selected from the group consisting of alkyl, aryl, and alkarylradicals, such alkyl radical containing from about 1 to about l0 carbonatoms, such aryl and alkaryl radicals containing from about 6 to about15 carbon atoms, and n is an integer of from I to 3.

Thus, where R is alkyl, such alkyl radical can be straight chain orbranched chain, and can include methyl, ethyl, propyl, isopropyl, butyl,isobutyl, amyl, isoamyl, hexyl, isohexyl, octyl, isooctyl, nonyl,isononyl, decyl and isodecyl. Examples of alkyl, iodides which aresuitable include methyl iodide, ethyl iodide, isopropyl iodide, n-butyliodide, n-hexyl iodide, nnonyl iodide, l,4-diiodobutane,Lo-diiodohexane, 1,9- diiodononane, l l O-diiododecane, l ,4,7-triiodoheptane, 1,6,lO-triiododecane, and 2,4,6- triiodooctane. Alkyliodides wherein n is l to 2 are preferred.

Aryl iodides which can be employed include iodo compounds of the aboveformula wherein R can be phenyl, biphenyl, and naphthyl. Examples ofsuch aryl iodides include 4-iodobiphenyl, Z-iodobiphenyl, 4,4-diiodobiphenyl, 2,4,4-triiodobiphenyl, iodobenzene, l,4-diiodobenzene,l-iodonaphthalene, 2- iodonaphthalene, l,4-diiodonaphthalene, l,4,8-triiodonaphthalene, and l,3,5-trii.odonaphthalene. Of the aryl iodides,those wherein n is l to 2 are also preferred, the monoiodides thereofbeing found particularly advantageous.

The alkaryl iodides which can be employed include alkyl phenyl, alkylbiphenyl, and alkyl naphthalene compounds. The alkyl portion of suchalkaryl compounds can contain from 1 to about 9 carbon atoms, eitherstraight chain or branched chain, e.g., methyl, ethyl, propyl,isopropyl, butyl, amyl or pentyl, hexyl, heptyl, octyl or nonyl. Therecan be one or more alkyl groups connected to an aryl, e.g. phenyl orbiphenyl nucleus. Thus, such alkaryl radicals can include tolyl, xylyl,ethyl phenyl, propyl phenyl, isopropyl phenyl, methyl naphthyl, ethylnaph'thyl, methyl biphenyl, ethyl biphenyl, 4,4-diethyl biphenyl, andthe like. One to three iodo radicals can be connected either to the arylnucleus or the alkyl substituent on the aryl nucleus, preferably theformer. Examples of alkaryl additives which can be employed include2-iodotoluene, 4- iodotoluene, 4-iodoethyl-benzene, 4-iodo ortho xylene,5- iodo meta xylene, 2-iodo para xylene, mixtures of such iodo xylenecompounds which can be produced by iodinating a commercial xylenemixture, 4-iodo isopropyl benzene, benzyl iodide, l-iodo-4-methyl,naphthalene, l-iodo-4-ethyl naphthalene, 4-iodo-4' -methyl biphenyl,4-iodo-4'-isopropyl biphenyl, l,5-diiod0-2,6- dimethyl naphthalene,l,8-diiodo-4,5-dimethyl naphthalene, and l,4,5-triiodo-8-methylnaphthalene.

.Aryl iodides which have been found particularly effective are4-iodobiphenyl and l-iodonaphthalene.

Functional fluids whose flammability characteristics are substantiallyimproved by incorporation of the organic iodo compounds according to theinvention, are base stocks consisting essentially of a member selectedfrom the group consisting of a phosphate ester and a dicarboxylic acidester. These include a phosphate ester, mixtures of phosphase esters, adicarboxylic acid ester, mixtures of the latter esters, and particularlymixtures of a phosphate ester or esters and a dicarboxylic acid ester oresters.

Phosphates which can be employed according to the invention have thegeneral formula:

where R R and R; can be the same or different, and each can be aryl suchas phenyl'and naphthyl, alkaryl such as cresyl, xylyl, ethyl phenyl,propyl phenyl, isopropyl phenyl, and the like, said aryl and alkarylradicals preferably containing from 6 to about 8 carbon atoms, alkyl,both straight chain and branched chain of from about 3 to about 10carbon atoms such as npropyl, n-butyl, n-amyl, n-hexyl, isopropyl,isobutyl, and the like, and alkoxyalkyl having from about 3 to about 8carbon atoms such as methoxy methyl, methoxy ethyl, ethoxy ethyl,methoxy propyl, and the like.

Preferred phosphate esters are the dialkyl aryl, triaryl, trialkyl andalkyl diaryl phosphates.

Examples of such phosphate esters are the dialkyl aryl phosphates inwhich the alkyl groups are either straight chain or branched chain andcontain from about 3 to about 10 carbon atoms, such as n-propyl, nbutyl,n-amyl, n-hexyl, isopropyl, isobutyl, isoamyl, and the aryl radicalshave from 6 to 8 carbon atoms and can be phenyl, cresyl or xylyl,particularly dialkyl phenyl phosphates including dibutyl phenylphosphate, butyl amyl phenyl phosphate, butyl hexyl phenyl phosphate,butyl heptyl phenyl phosphate, butyl octyl phenyl phosphate, diamylphenyl phosphate, amyl hexyl phenyl phosphate, amyl heptyl phenylphosphate, and dihexyl phenyl phosphate.

Examples of triaryl phosphates which can be employed in the inventioncompositions are those in which the aryl radicals of such phosphateshave from 6 to 8 carbon atoms, that is, may be phenyl, cresyl or xylyl,

and in which the total number of carbon atoms in all three of the arylradicals is from 19 to 24, that is, in which the three radicals includeat least one cresyl or xylyl radical. Examples of such phosphatesinclude tricresyl, trixylyl, phenyl dicresyl, and cresyl diphenylphosphates.

Examples of trialkyl phosphates employed according to the inventioninclude phosphates having alkyl groups which are either straight chainor branched chain with from about 3 to about 10 carbon atoms, such asnpropyl, n-butyl, n-amyl and n-hexyl, particularly tri-nbutyl phosphate,tri(2-ethyl hexyl) phosphate, the straight chain alkyl groups preferablycontaining from 4 to 6 carbon atoms.

Examples of alkyl diaryl phosphates which can be employed to produce theinvention compositions include those in which the aryl radicals of suchphosphates may have from 6 to 8 carbon atoms and may be phenyl, cresylor xylyl, and the alkyl radical may have from about 3 to about 10 carbonatoms, examples of which are given above. Examples of the alkyl diarylphosphates include butyl diphenyl amyl diphenyl, hexyl diphenyl, heptyldiphenyl, octyl diphenyl, 6-methyl heptyl diphenyl, Z-ethylhexyldiphenyl, butyl phenyl cresyl, amyl phenyl xylyl, and butyl dicresylphosphates.

Any phosphate ester can be employed which is normally liquid betweenabout 65F and 2lOF. Preferably, the above-noted trialkyl phosphates anddialkyl aryl phosphates such as tributyl phosphate and dibutyl phenylphosphate, are employed, as such phosphates are particularly effectivein achieving low viscosity at low temperature. However, for improvedhigher viscosity at high'temperature of the order of 2lOF, it isdesirable to employ triaryl phosphates as illustrated above, e.g.,tricresyl phosphate, particularly in combination with the above-notedtrialkyl phosphates. Preferred phosphate ester mixtures are theabove-noted dialkyl aryl phosphates such as dibutyl phenyl phosphate, incombination with a trialkyl phosphate such as tributyl phosphate.

Another functional fluid base stock, the flammability or autoignitiontemperature of which is substantially increased according to theinvention is a dicarboxylic acid ester. Preferred types of the lattercompounds are the aliphatic dicarboxylic acid esters, particularly thealkyl diesters of adipic and sebacic acid, that is the diester adipatesand sebacates. Such esters can contain alkyl groups, either straightchain or branched chain, containing from about 4 to about 12 carbonatoms including butyl, isobutyl, amyl, pentyl, hexyl, isohexyl, nonyl,decyl and isodecyl groups. Specific examples of these diesters aredihexyl, di(2-ethyl-hexyl), dioctyl, dinonyl, didecyl and diisodecyladipate, and the corresponding sebacates. Of the above-describeddiesters of adipic and sebacic acid, diisodecyl adipate and diisodecylsebacate have been found particularly effective, especially diisodecyladipate, Also, the diesters of the aromatic dicarboxylic acids,particularly the diesters of phthalic acid, that is the phthalatediesters, can be employed as base stocks. The diesters of such aromaticacids can contain alkyl groups of from 4 to 12 carbon atoms, examples ofwhich are given above with respect to the diesters of the aliphaticdicarboxylic acids, adipic and sebacic acid. Illustrative examples ofthe diester phthalates which can be employed are di-n-butyl phthalate,dihexyl phthalate, dioctyl phthalate, dinonyl phthalate, didecylphthalate, and diisodecyl phthalate. Although the two ester, i.e.,alkyl, groups in the diesters described above are usually the same, suchester groups on a particular diester can be different, e.g., asillustrated by nonyl decyl adipate.

Mixtures of such dicarboxylic acid esters can also be employed, e.g. amixture of diisodecyl adipate and diisodecyl sebacate, or a mixture of adiestcr of an aromatic acid, e.g., a phthalic acid alkyl diester, and analiphatic acid alkyl diester such as an adipic or sebacic acid alkyldiester.

As previously noted, a functional fluid base stock consisting of amixture of a phosphate ester or esters, and a dicarboxylic acid ester oresters, particularly an aliphatic dicarboxylic acid ester, as describedabove, can be effectively improved with respect to increasing fireresistance of such base stock, by incorporation of an organic iodideadditive as described above, according to thejnvention. When suchmixtures are employed as base stock, generally a substantial proportionof both the phosphate ester and dicarboxylic acid diester, particularlyadipate diester, are employed. Thus, the amount of phosphate ester oresters present in such base stock mixtures can range, by weight, fromabout 35 to about 85%, preferably about 50 to about 80%, and the amountof dicarboxylic acid diester, e.g., adipate diester, sebacate diester,or mixture thereof, can range, by weight, from about 15 to about 65%,preferably about 20 to about 50%. Functional fluid compositionscomprising such mixtures of a phosphate ester or esters and adicarboxylic acid ester such as an adipic r sebacic acid alkyl diester,are described and claimed in my copending application Ser. No. 129,269,filed Mar. 29, I97]. These are preferred base stock mixtures.

Functional fluid compositions comprising a mixture, by weight, of about15 to about 75% ofa phosphate ester, about to about 75% of a phthalicacid alkyl diester containing alkyl groups of about 4 to about 12 carbonatoms and 0 to about 50% of an adipic or sebacic acid alkyl diester,having alkyl groups containing from about 4 to about 12 carbon atoms,described and claimed inmy copending application Ser. No. 129,270, filedMar. 29, 1971, now US. Pat. No. 3,795,620, can also be improvedsignificantly by addition thereto of an organic iodo compound accordingto the invention.

The disclosures of the base stocks of my above copending applicationsare incorporated herein by reference.

Where the above-noted mixtures of phosphate ester and dicarboxylic acidester are employed as base stock, in many instances suitable viscositycharacteristics both at low temperaturesbelow 40F and at hightemperatures above 2l0F can be achieved in the absence of a viscosityindex improver. However, it may be desirable, particularly for improvingpump life in a hydraulic system, to incorporate a small amount rangingfrom 0.1 to about 20%, generally about 2 to about by weight of thecomposition, of a viscosity index improver. Examples of the latter arepolyalkyl acrylates and polyalkyl methacrylates, in which the alkylgroups may contain from about 4 to about 12 carbon atoms, eitherstraight or branched chain, and having an average molecular weightranging from about 2,000 to about 15,000. Specific examples of suchviscosity index improvers are polybutyl methacrylate and poly n-hexylacrylate, having an average molecular weight ranging between about 2,000and about l2,000.

It will be understood that other commonly employed functional fluidadditives such as oxidation inhibitors, stabilizers, metal deactivators,and the like, such as epoxides, dialkyl sulfides, benzothiazole, phenylalpha naphthylamine and phenolic oxidation inhibitors, can beincorporated into the base stock.

For greatest effectiveness in substantially reducing the flammability,and for correspondingly substantially increasing the autoignitiontemperature of the above functional fluid base stocks according to theinvention, it is usually desirable to employ only a small amount of theinvention additive, that is, alkyl or aryl, including alkaryl, iodide,as defined above, in the functional or hydraulic fluid base stock.Generally, there can be employed as little as 0.1% and up to about 5%ofthe alkyl iodide or aryl iodide additive of the invention, preferablyfrom about 0.5 to about 2.5% of such iodide additive, in the functionalfluid base stock, based on the weight of the composition.

The following are examples illustrating practice of the invention byincorporation of the alkyl and aryl iodides described herein asadditives according to the invention, into functional fluid base stocksof the types described above. In the examples below, the term AIT meansautoignition temperature, the autoignition temperature of the functionalfluid compositions ofthe invention according to the examples below beingdetermined in accordance with standard methods of test for autoignitiontemperature according to ASTM D 2155 procedure. All percentages are interms of per cent by weight of the functional fluid composition.

EXAMPLE I To tri-n-butyl phosphate are added varying amounts of4-iodobiphenyl, and the autoignition temperature of the various fluidcompositions and of a control oftri-nbutyl phosphate with no iodocompound, is obtained.

The results of such tests are noted in the table below.

TABLE I Additive Fluid Additive Concentration ('71) AIT (F) tri-n butyl4-iodobiphenyl 0 730 phosphate do. do. 1.0 8 I0 do. do. 15 900 do. do.2.0 880 EXAMPLE 2 The procedure of Example 1 is repeated exceptemploying in place of 4-iodobiphenyl, l-iodonaphthalane in aconcentration of 1% and l.5% respectively in the tri-n-butyl phosphate.

The data and results are set forth in Table II below.

TABLE ll Additive Fluid 7 Additive Concentration AlT (F) tri-n-butyll-iodonaphthalene (l 730 phosphate y do. do. I.() 800 do. do. l.5 940From Table II above, it is noted that incorporation of 1.0% of theiodonaphthalene additive increase AlT from the 730F of the control to800F, and increasing concentration t'o'l.5% of'suc'h iodo additivesubstan tially increases AlT to 940F as compared to the 730F value forthe control.

EXAMPLE 3 The following composition is prepared.

Fluid A Weight 71.

tri-n-butyl phosphate 49.4 di-n-butyl phenyl phosphate 8.9 diisodecyladipate 32.6 poly n-hexyl acrylatc viscosity index improver, m.w. 2,000(Ucon F.H.25) 4.4 diepoxide oxidation inhibitor (Unox 22] 2.24-iodobiphcnyl 2.0 water Q l(l().0

The autoignition temperatures of Fluid A and of a control of Fluid A inthe absence of any iodo compound are obtained, the AlT of Fluid Acontaining the 52.0% of 4-iodobiphenyl being 810F, more than 200Fgreater than the MT of less than 600F for the control.

Results of closed oxidation-corrosion tests at 250F for 168 hours areset forth in Tables lll and IV below, the metals of Table III all beinginserted in the same fluid noted above and designated Fluid A, in onetest,

and the metals of Table IV all being inserted in another portion ofFluid A in another test, the acid number of the Fluid A in each of thetests being determined after I the l 68 hour test period.

EXAMPLE 4 The procedure of Example 3 is repeated, except employing inplace of 2% of 4-iodobiphenyl in Fluid A, 2%

of l-iodo-naphthalene.

An increase in AlT of the resulting fluid from an AlT of less than 600Ffor the control, to about 790F for the fluid containing the aboveconcentration of liodonaphthalene is achieved.

Also, substantially similar results are obtained with respect tosubstantial freedom from corrosive attack on the metals of Tables Illand IV, by the fluid containing the l-iodonaphthalene, comparable to theresults obtained in'Example 3.

EXAMPLE 5 The following functional fluid compositions B, C, D and E areprepared, and their respective autoignition temperatures obtained.

Composition B Components /1 by weight dibutyl phenyl phosphate 99.2

'4.4-diiodobiphenyl 0.8

Composition C dioetyl scbaeate 97.8

n-hcxyl iodide 22 Composition D di-(Z-ethylhexyl) phenyl phosphate 49diisodecyl adipatc 49 2-iodohiphcnyl 2 Composition E tri cresylphosphate 4) diisodecyl phthalatc 49 iodobcnzenc 2 In each case theincorporation of the respective iodo compounds into the functional fluidbase stock of functional fluid compositions, B, C, D and E above, sub-;stantially increases autoignition temperature to between about 800 and950F, as compared to the MT of less than 750F for each of the respectivefunctional fluid base stocks of compositions B through E, in the absenceof the iodo compound, the MT of the resulting fluid generally increasingin relation to the increase in From Tables Ill and IV above, it is seenthat Fluid A shows practically complete freedom from corrosive attack onthe metals of such tables, except for magnesium, although the relativelysmall corrosive value in Table III for magnesium is well within aircraftspecification standards, and a low acid number for Fluid A is obtainedin both tests reported in Tables Ill and IV.

concentration between 6.8 to 2.2% of the iodo compounds of compositionsB through E.

EXAMPLE 6 The functional fluid compositions F. G, H and .l set forthbelow are prepared, and their autoignition temperatures obtained, inrelation to the autoignition temperature of the respective compositionsin the absence of the recited iodo compounds.

Composition F Components '/1 by weight diisodecyl adipate 60 diisodecylphthalate 37.5

l-iodonaphthalene 2.5

Composition J phenyl dicresyl phosphate 58 diisodecyl adipate 38l,9-diiodo nonane 4 For each of the compositions F, G, H and 1 above,the autoignition temperature is substantially increased to the range ofbetween 800 and 950F in the presence of the iodo compounds therein, ascompared to corresponding autoignition temperatures of less than 700Ffor the respective compositions F, G, H and J, in the absence of therespective iodo compounds therein, the AIT of the compositions F, G, Hand J generally varying in relation to the concentration of iodocompound therein, the AIT of composition J containing the relativelyhigh concentration of 4% of iodo compound therein however not beingsubstantially greater than that for composition G containing 3% of theiodo compound thereof.

EXAMPLE 7 Functional fluid compositions K. L, M. N and 0, set forthbelow, are prepared, and the autoignition temperatures of suchcompositions in relation to their controls, in the absence of therespective iodo compounds, are obtained.

Composition K Components by weight tri-n-butyl phosphate 80 tri cresylphosphate l7 diiodohexane 3 Composition L The autoignition temperatureobtained for each of compositions K through above is substantiallyincreased and in the range of about 800 to about 950F,

as compared to autoignition temperatures of less than 750F, for therespective compositions in the absence of the respective iodo compoundstherein. The autoignition temperatures of compositions K through 0 generally increases with respect to increase in concentration from the 0.5%of the iodo compound employed in compositions M and O, to the 3% of iodocompound employed in compositions K and N.

EXAMPLE 8 The procedure of Example 3 is repeated, except employing inplace of 4-iodobiphenyl in Fluid A, 2% of l,l()-diiododeeane in a firstfluid used in one series of tests, and 2% of n-hexyl iodide in a secondfluid used in a second series of tests.

An increase in AIT of the resulting fluids from an AIT of less than 600Ffor the control, to about 8 10F for the one fluid containingLEO-diiododecane and 780F for the other fluid containing n-hexyl iodideare obtained.

Also results comparable to those of Example 3 are obtained with respectto substantial freedom from corrosive attack on the metals of Tables Illand IV, employing said first and second fluids above.

The following example illustrates still other functional fluidcompositions containing an iodo compound additive according to theinvention.

From the foregoing, it is seen that the invention provides novelfunctional fluid compositions containing certain organic iodo compounds,more particularly certain alkyl or aryl iodides, which functionefficiently as flame retardants or flame inhibitors in functional fluidscontaining as base stock a phosphate ester or a dicarboxylic acid ester,or mixtures thereof, while at the same time rendering such fluidsessentially noncorrosive on certain metals, particularly iron, aluminum,

copper and titanium, widely employed as hydraulic fluid systemcomponents and engine components requiring lubrication, in jet-turbinepower plants of jet aircraft.

While many of the above-described functional fluids, e.g., those havingas base stock a phosphate ester such as tributyl phosphate, di-n-butylphosphate, or mixtures thereof, and which may also contain adicarboxylic acid ester such as diisodecyl adipate, are particularlyeffective for use as hydraulic fluids in jet aircraft, particularlybecause of their desirable viscosity characteristics, includingrelatively low viscosity at low temperature and relatively highviscosity at elevated temperature, many of the above-describedfunctional fluids are of particular utility as industrial functionalfluids, for example engine lubricants. Examples of the latter types offluids are those comprising a base stock composed of certain phosphatessuch as tricresyl phosphate, or those composed of a mixture of phosphateester with an aromatic acid diester such as dioctyl phthalate, or thosehaving a base stock composed essentially ofa dicarboxylic acid estersuch as diisodecyl adipate or diisodecyl phthalate, or mixtures thereof.Illustrative of such industrial type fluids are those of compositions C,E, H, J, M and N. Particularly effective aircraft hydraulic fluids arethose exemplified by Fluid A and compositions B, D, .l, K, L and M.

Applicant is aware of U.S. Pat. No. 3,287,275 which discloses theaddition of 2-iodobiphenyl to an organic phosphinate, for reducingcorrosion of such phosphinate on iron. However, there is no suggestionor teaching in this patent that the incorporation of a small amount ofan organic iodo compound into a composition having as base stock aphosphate ester, a dicarboxylic acid ester, or mixtures thereof,materially reduces the flammability of such base stock andcorrespondingly increases autoignition temperature thereof, while at thesame time functioning to reduce corrosion of such fluids on a variety ofmetals including the abovenoted copper, aluminum, titanium, bronze andcadmium plate.

While I have described particular embodiments of my invention forpurposes of illustration, it will be understood that various changes andmodifications within the spirit of the invention can be made, and theinvention is not to be taken as limited except by the scope of theappended claims.

I claim:

1. A functional fluid composition consisting essentially of a basestock, said base stock consisting essentially of a mixture of about 35to about 85% of a phosphate ester having the general formula:

wherein R R and R are each a member selected from the group consistingof aryl, alkaryl, alkyl of from about 3 to about carbon atoms, andalkoxyalkyl having from about 3 to about 8 carbon atoms, and about toabout 65% of a dicarboxylic acid ester selected from the groupconsisting of the alkyl diesters of adipic and sebacic acid, containingalkyl groups of from about 4 to about 12 carbon atoms, and an alkyldiester of phthalic acid containing alkyl groups of from about 4 to,about 12 carbon atoms, and mixtures thereof; and a small amount of anorganic iodo compound sufficient to enhance the autoignition temperatureof said base stock, said iodo compound being selected from the groupconsisting of aryl and alkaryl mono, di and triodides, said aryl andalkaryl radicals containing from about 6 to about l5 carbon atoms.

2. A functional fluid composition as defined in claim 1, wherein saidiodo compound is an aryl iodide.

3. A functional fluid composition as defined in claim 1, wherein saidphosphate ester is selected from the group consisting of dialkyl aryl,triaryl, trialkyl, and alkyl diaryl phosphate.

4. A functinal fluid composition as defined in claim 1, saiddicarboxylic acid ester being selected from the group consisting ofadipic and sebacic acid alkyl diesters, having alkyl groups containingfrom about 4 to about 12 carbon atoms.

5. A functionalfluid composition defined in claim 1, said base stockconsisting essentially of a mixture of about 35 to about 85% of aphosphate ester selected from the group consisting of dialkyl aryl,triaryl, trialkyl, and alkyl diaryl phosphate, and about 15 to about 65%of a dicarboxylic acid ester selected from the group consisting ofadipic and sebacic acid alkyl diesters, having alkyl groups containingfrom about 4 to about 12 carbon atoms. by weight.

6. A functional fluid composition as defined in claim 5, wherein saidiodo compound is selected from the group consisting of phenyl, biphenyland naphthyl iodides and wherein said iodo compound is present in anamount ranging from about 0.1 to about 5% by weight of said composition.

7. A functional fluid composition as defined in claim 6, wherein saidphosphate ester is selected from the group cnsisting of tributylphosphate, dibutyl phenyl phosphate, tricresyl phosphate, and mixturesthereof, and said dicarboxylic acid ester is diisodecyl adipate.

8. A functional fluid composition as defined in claim 5, wherein saidiodo compound is selected from the group consisting of monoiodobiphenyl, monoiodo xylene and monoiodo naphthalene, and wherein saidiodo compound is present in an amount ranging from about 0.5 to about2.5%, by weight of said composition.

9. A functional fluid composition as defined in claim 8, said base stockconsisting essentially of a mixture of tributyl phosphate, dibutylphenyl phosphate and diisodecyl adipate, and wherein said iodo compoundis selected from the group consisting of 4-iodobiphenyl andl-iodonaphthalene.

10. A functional fluid composition as defined in claim 1, wherein saidiodo compound is present in an amount ranging from about 0.1 to about5%, by weight of said composition.

11. A functional fluid composition as defined in claim 2, wherein saidiodo compound is selected from the group consisting of monoiodobiphenyl, monoiodo xylene and monoiodo naphthalene.

12. A functional fluid composition as defined in claim 10, saiddicarboxylic acid ester being a mixture ofa diester selected from thegroup consisting of adipic and sebacic acid alkyl diesters, having alkylgroups containing from about 4 to about 12 carbon atoms, and a phthalicacid alkyl diester containing alkyl groups of from about 4 to about 12carbon atoms.

13. A functional fluid composition as defined in claim 10, said basestock consisting essentially ofa mix-. ture of about 50 to about of aphosphate ester selected from the group consisting of dialkyl aryl,triaryl, trialkyl, and alkyl diaryl phosphate, and about 20 to about 50%of a dicarboxylic acid ester selected from the group consisting ofadipic and sebacic acid alkyl diesters, having alkyl groups containingfrom about 4 to about 12 carbon atoms, by weight.

14. A functional fluid composition as defined in claim 10, wherein saidiodo compound is present in an amount ranging from about 0.5 to about2.5%, by weight of said composition.

15. A functional fluid composition as defined in claim 14, wherein saidphosphate ester is selected from the group consisting of dialkyl aryl,triaryl, trialkyl, and alkyl diaryl phosphate, said dicarboxylic acidester being selected from the group consisting of adipic and sebacicacid alkyl diesters, having alkyl groups containing from about 4 toabout 12 carbon atoms.

16. A functional fluid composition as defined in claim 10, wherein saidiodo compound is selected from the group consisting of phenyl, biphenyland naphthyl iodides.

17. A functional fluid composition as defined in claim 16, wherein saidiodo compound is a monoiodide.

18. A functional fluid composition as defined in claim 10, wherein saidphosphate ester is selected from the group consisting of dialkyl aryl,triaryl, trialkyl, and alkyl diaryl phosphate.

19. A functional fluid composition as defined in claim 18, wherein saidiodo compound is selected from the group consisting of phenyl, biphenyland naphthyl iodides.

20. A functional fluid composition as defined in claim 18, wherein saidiodo compound is selected from the grup consisting of monoiodo biphenyl,monoiodo xylene and monoiodo naphthalene.

21. A functional fluid composition consisting essentially of a basestock, said base stock consisting essentially of a member selected fromthe grup consisting of (a) a phosphate ester having the general formula:

where R R and R are each a member selected from the group consisting ofaryl, alkaryl, alkyl of from about boxylic acid ester selected from thegroup consisting of the alkyl diesters of adipic and sebacic acid,containing alkyl groups of from about 4 to about 12 carbon atoms, and analkyl diester of phthalic acid containing alkyl groups of from about 4to about 12 carbon atoms, and mixtures thereof; and a small amount of anorganic iodo compound sufficient to enhance the autoignition temperatureof said base stock, said iodo compound being selected from the grupconsisting of aryl and alkaryl mono, di and triodides, said aryl andalkaryl radicals containing from about 6 to about 15 carbon atoms.

22. A functional fluid composition as defined in claim 21, wherein saidiodo compound is an aryl iodide.

23. A functional fluid composition as defined in claim 21, wherein saidiodo compound is present in an amount ranging from about O.l to about5%, by weight of said composition.

24. A functional fluid composition as defined in claim 23, wherein saidiodo compound is present in an amount ranging from about 0.5 to about2.5%, by weight of said composition.

25. A functional fluid composition as defined in claim 23, wherein saidiodo compund is selected from the group consisting of monoido biphenyl,monoiodo xylene and monoiodo naphthalene.

26. A functional fluid composition as defined in claim 23, wherein saidiodo compound is selected from the group consisting of phenyl, biphenyland naphthyl iodides.

27. A functional fluid composition as defined in claim 26, wherein saidiodo compound is a monoiodide.

2. A functional fluid composition as defined in claim 1, wherein saidiodo compound is an aryl iodide.
 3. A functional fluid composition asdefined in claim 1, wherein said phosphate ester is selected from thegroup consisting of dialkyl aryl, triaryl, trialkyl, and alkyl diarylphosphate.
 4. A functinal fluid composition as defined in claim 1, saiddicarboxylic acid ester being selected from the group consisting ofadipic and sebacic acid alkyl diesters, having alkyl groups containingfrom about 4 to about 12 carbon atoms.
 5. A functional fluid compositionas defined in claim 1, said base stock consisting essentially of amixture of about 35 to about 85% of a phosphate ester selected from thegroup consisting of dialkyl aryl, triaryl, trialkyl, and alkyl diarylphosphate, and about 15 to about 65% of a dicarboxylic acid esterselected from the group consisting of adipic and sebacic acid alkyldiesters, having alkyl groups containing from about 4 to about 12 carbonatoms, by weight.
 6. A functional fluid composition as defined in claim5, wherein said iodo compound is selected from the group consisting ofphenyl, biphenyl and naphthyl iodides and wherein said iodo compound ispresent in an amount ranging from about 0.1 to about 5% , by weight ofsaid composition.
 7. A functional fluid composition as defined in claim6, wherein said phosphate ester is selected from the group cnsisting oftributyl phosphate, dibutyl phenyl phosphate, tricresyl phosphate, andmixtures thereof, and said dicarboxylic acid ester is diisodecyladipate.
 8. A functional fluid composition as defined in claim 5,wherein said iodo compound is selected from the group consisting ofmonoiodo biphenyl, monoiodo xylene and monoiodo naphthalene, and whereinsaid iodo compound is present in an amount ranging from about 0.5 toabout 2.5%, by weight of said composition.
 9. A functional fluidcomposition as defined in claim 8, said base stock consistingessentially of a mixture of tributyl phosphate, dibutyl phenyl phosphateand diisodecyl adipate, and wherein said iodo compound is selected fromthe group consisting of 4-iodobiphenyl and 1-iodonaphthalene.
 10. Afunctional fluid composition as defined in claim 1, wherein said iodocompound is present in an amount ranging from about 0.1 to about 5%, byweight of said composition.
 11. A functional fluid composition asdefined in claim 2, wherein said iodo compound is selected from thegroup consisting of monoiodo biphenyl, monoiodo xylene and monoiodonaphthalene.
 12. A functional fluid composition as defined in claim 10,said dicarboxylic acid ester being a mixture of a diester selected fromthe group consisting of adipic and sebacic acid alkyl diesters, havingalkyl groups containing from about 4 to about 12 carbon atoms, and aphthalic acid alkyl diester containing alkyl groups of from about 4 toabout 12 carbon atoms.
 13. A functional fluid composition as defined inclaim 10, said base stock consisting essentially of a mixture of about50 to about 80% of a phosphate ester selected from the group consistingof dialkyl aryl, triaryl, trialkyl, and alkyl diaryl phosphate, andabout 20 to about 50% of a dicarboxylic acid ester selected from thegroup consisting of adipic and sebacic acid alkyl diesters, having alkylgroups containing from about 4 to about 12 carbon atoms, by weight. 14.A functional fluid composition as defined in claim 10, wherein said iodocompound is present in an amount ranging from about 0.5 to about 2.5%,by weight of said composition.
 15. A functional fluid composition asdefined in claim 14, wherein said phosphate ester is selected from thegroup consisting of dialkyl aryl, triaryl, trialkyl, and alkyl diarylphosphate, said dicarboxylic acid ester being selected from the groupconsisting of adipic and sebacic acid alkyl diesters, having alkylgroups containing from about 4 to about 12 carbon atoms.
 16. Afunctional fluid composition as defined in claim 10, wherein said iodocompound is selected from the group consisting of phenyl, biphenyl andnaphthyl iodides.
 17. A functional fluid composition as defined in claim16, wherein said iodo compound is a monoiodide.
 18. A functional fluidcomposition as defined in claim 10, wherein said phosphate ester isselected from the group consisting of dialkyl aryl, triaryl, trialkyl,and alkyl diaryl phosphate.
 19. A functional fluid composition asdefined in claim 18, wherein said iodo compound is selected from thegroup consisting of phenyl, biphenyl and naphthyl iodides.
 20. Afunctional fluid composition as defined in claim 18, wherein said iodocompound is selected from the grup consisting of monoiodo biphenyl,monoiodo xylene and monoiodo naphthalene.
 21. A functional fluidcomposition consisting essentially of a base stock, said base stockconsisting essentially of a member selected from the grup consisting of(a) a phosphate ester having the general formula:
 22. A functional fluidcomposition as defined in claim 21, wherein said iodo compound is anaryl iodide.
 23. A functional fluid composition as defined in claim 21,wherein said iodo compound is present in an amount ranging from about0.1 to about 5%, by weight of said composition.
 24. A functional fluidcomposition as defined in claim 23, wherein said iodo compound ispresent in an amount ranging from about 0.5 to about 2.5%, by weight ofsaid composition.
 25. A functional fluid composition as defined in claim23, wherein said iodo compund is selected from the group consisting ofmonoido biphenyl, monoiodo xylene and monoiodo naphthalene.
 26. Afunctional fluid composition as defined in claim 23, wherein said iodocompound is selected from the group consisting of phenyl, biphenyl andnaphthyl iodides.
 27. A functional fluid composition as defined in claim26, wherein said iodo compound is a monoiodide.